Dichotomous key builder sim

What the sim shows

A field-study bench: eight small animals in clear specimen pots on damp filter paper, drawn true size (beetle 15 mm, ant 5 mm, spider 10 mm, woodlouse 12 mm, centipede 25 mm, millipede 20 mm, snail 35 mm, earthworm 90 mm), a ×10 hand lens on a stand, a key card on a clipboard, two new animals in a tray (ladybird 7 mm, slug 40 mm), a pooter and a soft paintbrush for moving animals gently. A dichotomous key is a list of couplets: each asks one yes/no question about a feature you can see, and each answer leads either to the next couplet or to a name. A key is valid when every question splits its group into two groups, neither empty, every animal reaches exactly one end with its own name, and it never goes round in a circle. The features: insects have 6 legs and a body in 3 parts (head, thorax, abdomen); spiders have 8 legs, 2 body parts and no antennae; woodlice 14 legs; centipedes one pair of legs on each segment, millipedes two pairs on most; snails, slugs and earthworms have no legs. A key only works for the animals it was made for: a new animal may reach the wrong name, and then the key needs another question. The close-up is drawn to fit its circle; its scale bar is true for the animal shown.

• Specimen pots: drag one under the hand lens, then answer each couplet (one click = one step)
• Key board: drag questions onto the tree, then drag each animal into its yes or no group
• New animals: test your key on them

Use it in your lessons

• Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
• Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
• Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.

Free guide: 12 practicals as sims, and how to run one in a lesson →

Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.